1. Field
The disclosed concept relates generally to electrical switching apparatus and, more particularly, to electrical switching apparatus, such as circuit breakers. The disclosed concept also relates to carrier assemblies for electrical switching apparatus.
2. Background Information
Electrical switching apparatus, such as circuit breakers, provide protection for electrical systems from electrical fault conditions such as, for example, current overloads, short circuits, abnormal voltage and other fault conditions. Typically, circuit breakers include an operating mechanism which opens electrical contact assemblies to interrupt the flow of current through the conductors of an electrical system in response to such fault conditions.
As shown in FIG. 1, the electrical contact assemblies of some circuit breakers include a movable contact assembly 1 having a plurality of movable contacts 3, which are movable into and out of electrical contact with corresponding stationary contacts (not shown). Specifically, the movable contacts 3 are disposed on movable contact arms or fingers 5, which are pivotably coupled to a carrier assembly 7 (see also FIGS. 2A and 2B). The carrier assembly 7 includes a plurality of contact springs 9, shown in FIGS. 2A and 2B, which are structured to bias the fingers 5 (FIG. 1) and corresponding movable contacts 3 (FIG. 1) disposed thereon against the stationary contacts (not shown) in order to provide and maintain contact pressure when the circuit breaker is closed, and to accommodate wear. The carrier assembly 7 also includes a plurality of blow off springs 11 (also sometimes referred to as cam springs) (best shown in the exploded view of FIG. 2B), which are structured to reduce circuit breaker fault clearing times. That is, the carrier assembly 7 is designed to be current-limiting such that the movable contacts 3 (FIG. 1) of the movable contact assembly 1 “blow off” (e.g., separate from) the corresponding stationary contacts (not shown) under relatively high current fault conditions.
Among other disadvantages, such carrier assembly designs include numerous parts and are relatively difficult to assemble. For example and without limitation, as shown in the example of FIGS. 2A and 2B, the carrier assembly 7 includes as many as 20 or more contact springs 9, which are difficult to assemble and difficult to properly align with the corresponding fingers 5 (FIG. 1) of the assembly carrier assembly 7. Improper alignment results in inconsistent spring force, and a lower than desired withstand rating for the circuit breaker. Such carrier assembly designs are also sensitive to dimensional variations among the various components of the carrier assembly 7 which, on one hand, can result in undesirably low blow off forces (e.g., nuisance blow where unintended electrical disconnection occurs) and, on the other hand, can contribute to undesirably high blow off forces potentially leading to higher than desired current being let through the circuit breaker and causing damage to the circuit breaker.
Furthermore, to ensure that the circuit breaker will function properly in service, certain carrier assemblies (e.g., 7) are tested to verify that the required blow off force is within predetermined upper and lower limits. Therefore, such carrier assemblies are rejected if they do not fall within the prescribed upper and lower limits. It is desirable to minimize the number of rejections in order to maximize production yield, particularly in view of the relatively high cost of the carrier assembly (e.g., 7).
There is, therefore, room for improvement in electrical switching apparatus, such as circuit breakers, and in carrier assemblies therefor.